The present invention has particular application in an electric motor of the type with an external rotor and an internal stator, in particular a permanent magnet direct-current brushless type motor. More specifically the invention is directed to a rotor of the type comprising a carrier structure including a disc portion to which is centrally connected a hub, and the periphery of which is joined to a basically annular cylindrical skirt portion which in use extends coaxially around the stator.
This type of rotor for a brushless D.C. motor typically carries, in the annular skirt part, a plurality of permanent magnets, and an associated structure for linking up the magnetic flux produced by these magnets.
In a brushless electric motor of this construction, the stator has a magnetically conducting structure in a star geometry, with a plurality of radial expansions or teeth, supporting coils that form the stator windings. Typically at least one card or board containing the components of an electronic control circuit are attached to the stator, usually on the opposite side from the rotor. These components generate heat during use and add to the heat generated by the stator windings.
There is a desire to provide a rotor of the type specified above, capable of contributing significantly to the cooling of the stator windings and of the electronic control circuit connected to the motor.